1. Field of the Invention
The present invention relates to a compressor and more specifically to a turbo compressor for a gas turbine or the like, equipped with an improved surge limit suppressing arrangement.
2. Description of the Prior Art
In order to suppress or lower the surge limit of a turbo compressor it is know to swirl the inducted air flow upstream of the turbo compressor wheel when the induction volume falls to a level at which surging is apt to occur. This reduces the angle of incidence of the incomming flow of air on the blades of the compressor wheel suppressing the surge limit.
A known arrangement utilized for controllably swirling the incomming flow of air upstream of the turbo compressor wheel 1 is shown in FIGS. 1 and 2. This arrangement takes the form of a series of equidistantly spaced vanes 2 disposed radially about the axis of rotation of the turbo compressor 1. Each of the vanes 2 is pivotally mounted on a shaft 3 provided at one end with a connection link or lever 4. A ring member 5 is operatively connected to each of the links 4 and so that upon rotation of same each of the vanes 2 undergoes the same degree of deflection from its home or neutral position. However, when this arrangement is applied to the illustrated type of gas turbine, viz., a gas turbine having an induction port asymmetrical with respect to the axis of rotation of the turbo compressor wheel wherein the port lies in an essentially flat plane which is tangential to and non-intersecting with the turbo compressor wheel axis, the flow path from the "asymmetrical" induction port to the guide vanes closest thereto is shorter than those successively spaced therefrom. Further, due to the configuration of the induction port the angle of entry of the flows between the vanes tends to vary along with the generation of a flow velocity differential between adjacent vanes. These flow velocity differentials between the vanes tends to induce the situation wherein the flow velocity on one side of a vane is different from that on the other, whereupon a pressure differential occurs at the trailing edge of the vane which in turn produces turbulent or eddy flow downstream thereof. This turbulent flow creates a vibration which under given operational conditions tends to maximize or resonate to the degree of damaging the blades 6 of the compressor. Moreover, the differing angles of entry of the flows between the vanes induces the situation wherein the angle of incidence of the air on the blades of the compressor is not uniform and accordingly deviates across the face of the compressor wheel from the desired value for any given low induction mode of operation.
Moreover, the construction of the just described arrangement is complex and difficult to install in the confined space available in an induction housing having an "asymmetrical" port.